Wireless communication systems are well known in the art. Communications standards are developed in order to provide global connectivity for wireless systems and to achieve performance goals in terms of, for example, throughput, latency and coverage. One current standard in widespread use, called Universal Mobile Telecommunications Systems (UMTS), was developed as part of Third Generation (3G) Radio Systems, and is maintained by the Third Generation Partnership Project (3GPP).
A typical UMTS system architecture in accordance with current 3GPP specifications is depicted in FIG. 1. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an Iu interface. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit receive units (WTRUs), referred to as user equipments (UEs) in the 3GPP standard, via a Uu radio interface. A commonly employed air interface defined in the UMTS standard is wideband code division multiple access (W-CDMA). The UTRAN has one or more radio network controllers (RNCs) and base stations, referred to as Node Bs by 3GPP, which collectively provide for the geographic coverage for wireless communications with UEs. One or more Node Bs is connected to each RNC via an Iub interface; RNCs within a UTRAN communicate via an Iur interface.
The Uu radio interface of a 3GPP system uses Transport Channels (TrCHs) for transfer of user data and signaling between UEs and Node Bs. In 3GPP communications, TrCH data is conveyed by one or more physical channels defined by mutually exclusive physical resources, or shared physical resources in the case of shared channels. TrCH data is transferred in sequential groups of Transport Blocks (TBs) defined as Transport Block Sets (TBSs). Each TBS is transmitted in a given Transmission Time Interval (TTI) which may span a plurality of consecutive system time frames. For example, according to the 3GPP UMTS Release '99 (R99) specification, a typical system time frame is 10 microseconds and TTIs are specified as spanning 1, 2, 4 or 8 of such time frames. According to high speed downlink packet access (HSDPA), an improvement to the UMTS standard part of Release 5 specifications, and high speed uplink packet access (HSUPA), part of Release 6 specifications, TTIs are typically 2 ms and therefore are only a fraction of a system time frame.
The processing of TrCHs into a Coded Composite TrCH (CCTrCH) and then into one or more physical channel data streams is explained, for example, with respect to time division duplex (TDD) communications in 3GPP TS 25.222. Starting with the TBS data, Cyclic Redundancy Check (CDC) bits are attached and Transport Block concatenation and Code Block segmentation is performed. Convolution coding or turbo coding is then performed, but in some instances no coding is specified. The steps after coding include radio frame equalization, a first interleaving, radio frame segmentation and rate matching. The radio frame segmentation divides the data over the number of frames in the specified TTI. The rate matching function operates by means of bit repetition or puncturing and defines the number of bits for each processed TrCH which are thereafter multiplexed to form a CCTrCH data stream.
In a conventional 3GPP system, communications between a UE and a node B are conducted using a single CCTrCH data stream, although the node B may be concurrently communicating with other UEs using respective other CCTrCH data streams.
The processing of the CCTrCH data stream includes bit scrambling, physical channel segmentation, a second interleaving and mapping onto one or more physical channels. The number of physical channels corresponds to the physical channel segmentation. For uplink transmissions, UE to Node B, the maximum number of physical channels for transmission of a CCTrCH is currently specified as two. For downlink transmissions, Node B to UEs, the maximum number of physical channels for transmission of a CCTrCH is currently specified as sixteen. Each physical channel data stream is then spread with a channelization code and modulated for over air transmission on an assigned frequency.
In the reception/decoding of the TrCH data, the processing is essentially reversed by the receiving station. Accordingly, UE and Node B physical reception of TrCHs require knowledge of TrCH processing parameters to reconstruct the TBS data. For each TrCH, a Transport Format Set (TFS) is specified containing a predetermined number of Transport Formats (TFs). Each TF specifies a variety of dynamic parameters, including TB and TBS sizes, and a variety of semi static parameters, including TTI, coding type, coding rate, rate matching parameter and CRC length. The predefined collection of TFSs for the TrCHs of a CCTrCH for a particular frame is denoted as a Transport Format Combination (TFC). For each UE a single TFC is selected per TTI so that there is one TFC processed per TTI per UE.
Receiving station processing is facilitated by the transmission of a Transport Format Combination Indicator (TFCI) for a CCTrCH. For each TrCH of a particular CCTrCH, the transmitting station determines a particular TF of the TrCH's TFS which will be in effect for the TTI and identifies that TF by a Transport Format Indicator (TFI). The TFIs of all the TrCHs of the CCTrCH are combined into the TFCI. For example, if two TrCHs, TrCH1 and TrCH2, are multiplexed to form CCTrCH1, and TrCH1 has two possible TFs, TF10 and TF11, in its TFS and TrCH2has four possible TFs, TF20, TF21, TF22, and TF23, in its TFS, valid TFCIs for CCTrCH1 could include (0,0), (0,1), (1,2) and (1,3), but not necessarily all possible combinations. Reception of (0,0) as the TFCI for CCTrCH1 informs the receiving station that TrCH1 was formatted with TF10 and TrCH2 was formatted with TF20 for the received TTI of CCTrCH1; reception of (1,2) as the TFCI for CCTrCH1 informs the receiving station that TrCH1 was formatted with TF11 and TrCH2 was formatted with TF22 for the received TTI of CCTrCH1.
In UMTS specification releases 5 and 6 pertaining to HSDPA and HSUPA, respectively, fast retransmissions are accomplished according to hybrid automatic repeat request (HARQ). There it is currently specified that only one hybrid automatic repeat request (HARQ) process is used per TTI.
High speed packet access evolution (HSPA+) and universal terrestrial radio access (UTRA) and UTRAN long term evolution (LTE) are part of a current effort lead by 3GPP towards achieving high data-rate, low-latency, packet-optimized system capacity and coverage in UMTS systems. In this regard, both HSPA+ and LTE are being designed with significant changes to existing 3GPP radio interface and radio network architecture. For example, in LTE, it has been proposed to replace code division multiple access (CDMA) channel access, used currently in UMTS, by orthogonal frequency division multiple access (OFDMA) and frequency division multiple access (FDMA) as air interface technologies for downlink and uplink transmissions, respectively. The air interface technology proposed by HSPA+ is based on code division multiple access (CDMA) but with a more efficient physical (PHY) layer architecture which can include independent channelization codes distinguished with respect to channel quality. Both the LTE and HSPA+ are being designed for multiple-input multiple-output (MIMO) communications physical layer support. In such new systems, multiple data streams can be used for communications between a UE and a Node B.
The inventors have recognized that the existing 3GPP medium access control (MAC) layer procedures are not designed to deal with the new PHY layer architectures and features of the proposed systems. TFC selection in the current UMTS standard does not take into account some of the new transport format (TF) attributes introduced by LTE and HSPA+ including, but not limited to, time and frequency distribution and number of subcarriers in LTE, channelization codes in HSPA+, and different antenna beams in the case of MIMO.
According to the MAC procedures defined in the current UMTS standard, data multiplexed into transport blocks is mapped to a single data stream at a time, such that only one transport format combination (TFC) selection process is required to determine the necessary attributes for transmission over the physical channel starting at a common transmission time interval (TTI) boundary. Accordingly, only one hybrid automatic repeat request (HARQ) process, which controls data retransmissions for error correction, is allocated for any given UE-Node B communication. According to the proposed PHY layer changes for HSPA+ and UMTS described above, for a given UE-Node B communication, multiple physical resource groups may be available simultaneously for data transmissions, resulting in potentially multiple data streams to be transmitted for the communication.
The inventors have recognized that, starting at a common TTI boundary, multiple data streams may each have common or different quality of service (QoS) requirements, requiring specialized transmission attributes, such as modulation and coding, and different hybrid automatic repeat request (HARQ) processes. By way of example, in the case of multiple-input multiple-output (MIMO) communications, independent data streams can be transmitted simultaneously because of spatial diversity; however, each spatially diverse data stream requires its own transmission attributes and HARQ process to meet its desired QoS requirements because of different channel characteristics. There are currently no MAC methods or procedures to assign attributes to multiple data streams simultaneously and to effectively provide equal or unequal QoS to parallel data streams.
The inventors have developed a method for selecting multiple transport formats in parallel according to channel quality measurements and QoS requirements that exploits the new PHY layer attributes and features of HSPA+ and LTE systems.